Wind power as a source of green and abundant energy is often suggested as one of the most promising power sources and has acquired a great momentum across the world. In the last few decades, wind turbines with different generators have been developed to increase the maximum power capture, minimize the cost, and expand the use of the wind turbines in both onshore and offshore applications.
Wind turbines, or wind turbine generators (WTGs), have over the past decades therefore experienced an increasing importance in electrical power production, and this growth of power generated from WTGs is expected to continue due to the world-wide transition from fossil fuel, i.e. coal, oil, and gas, to more climate-neutral electricity production.
A wind turbine converts wind power into electrical energy through an electric generator driven by the blades of the wind turbine under windy conditions. In some wind turbines, the electric generator comprises a stator and a rotor both having multiphase windings, such as a double-fed induction generator (DFIG), a cascade-regulated generator, an induction or a synchronic generator, or a DC generator.
When having a rotor rotating in relation to a stator of a generator, electricity has to be transferred to or from the rotor. Electricity may be transferred by means of a slip ring assembly also called a rotary electrical interface, rotating electrical connector, collector, or swivel or electrical rotary joint, enabling the rotor to receive or return electricity while rotating in relation to the stator. When having a rotor with a multiphase winding, a control system within the wind turbine is able to regulate the frequency, so that the wind turbine produces at a predetermined frequency, e.g. approximately 50 Hz.
For a wind turbine with a doubly fed induction generator (DFIG), the rotor cables from the central part of the rotating shaft must be electrically connected to the rotor windings (normally 3 phases) on the periphery of the rotor. Due to the heating of the rotor, cables from high current and the high rotational speed of the rotor special precautions are necessary.
The rotor cables are normally fixed by bolts and similar means, but experience shows that this configuration is not stable enough under prolonged operation and critical failures have in fact occurred from this resulting in a complete standstill of some WTGs. Due to the recent year's growth in number of installed WTGs and the corresponding importance for the power production, such standstill for a prolonged period of time is highly undesirable.
Hence, an improved method for repairing an electric generator would be advantageous, and in particular a more efficient and/or reliable method would be advantageous.